This invention relates to a tank system for accommodating aquatic life and a method therefor. The invention has particular, although not exclusive, utility in accommodating live fish including shellfish, and especially rock lobster and abalone for holding and display purposes.
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Present tank systems for accommodating rock lobster in particular, in a closed circuit system, essentially consist of a long tank filled with water in which a number of rock lobster are disposed, such as is shown in FIG. 1 of the drawings. At one end of the tank A is provided a prefilter B and a biofilter C of known design. At the other end of the tank A is a protein skimmer D and associated pipe circuitry. A rectangular arrangement of water suction lines E are disposed at the base of the tank A and are connected to a pump F via an inlet line G. The pump F in turn is connected to an outlet manifold H via a water outlet line I. The manifold H is provided with a series of nozzles for spraying water which is sucked from the bottom of the tank via the suction lines E into the prefilter B to pass through the biofilter C. The biofilter C is provided with a pair of discharge pipes J for discharging water filtered by the biofilter back into the holding tank A.
As shown in FIG. 1, the prefilter B is disposed above the biofilter C, which in turn is disposed above the tank A at the one end thereof.
This prior art tank system has several disadvantages associated with it:
1. The prefilter B is usually neglected because of its elevated position where it is difficult to access.
2. The clean water from the biofilter is discharged into the tank A at one end and due to the arrangement of the suction lines at the base directly below it, creates a vertical water flow which is concentrated at the one end of the tank, short circuiting the flow of water throughout the tank.
3. There is not a uniform flow of clean water discharged into the tank via the discharge pipes J through to the other end of the tank and consequently dead spots are created within the tank.
4. Due to the biofilter size, shape and elevation relative to the tank, a large pump is necessary in order to draw a sufficient volume of water from the bottom of the tank, and deliver it to the prefilter B and biofilter C, so as to keep the biofilter charged with water continuously and the bacteria therein alive, particularly in the off season.
5. In order to clean the biofilter, the pump needs to be switched off and the biofilter drained, thereby killing the active bacteria within the biofilter.
6. There is no area for excess or overflow water from the tank to flow to, if the tank is heavily loaded with product, which is a natural tendency of users of the tank.
7. The tank system is not particularly portable, requiring it to be completely disassembled when transported.
It is an object of the present invention to provide for a more efficient and effective tank system for accommodating aquatic life than the type of prior art tank system described above.
It is a preferred object of the invention to provide for a uniform cross-flow of fluid in a tank system for the purposes of accommodating aquatic life therein.
In accordance with one aspect of the present invention, there is provided a tank system for accommodating aquatic life comprising:
a holding tank for holding fluid to sustain aquatic life disposed therein;
a filtering means for receiving extraneous fluid from the holding tank at one end of a filtering area and allowing the fluid to gravitate through a filtering medium disposed within the filtering area to another end of the filtering area;
tank discharge means to provide for the discharge and passage of the extraneous fluid from the top of the holding tank, along the substantial longitudinal extent of one side thereof, to the top of the filtering area at said one end thereof;
recirculating means for recirculating the extraneous fluid passed through the filtering means, from the other end of said filtering area to the holding tank, the recirculating means including tank inlet means for inletting fluid under pressure from the filtering means into the holding tank; and
said filtering means being disposed adjacent to the holding tank and the tank discharge means allowing for the natural flow of fluid from the top of the holding tank adjacent to said one side, to the top of the filtering area;
wherein the tank inlet means is disposed at the base of the holding tank, spaced from, and extending generally parallel, to the discharge means to provide for a uniform, circulatory cross-flow of fluid about a generally horizontal axis in substantially parallel relationship to said one side and to said tank inlet means, along the longitudinal extent of the holding tank and the tank discharge means.
Preferably, the tank inlet means has a rectilinear arrangement of inletting nozzles for jetting fluid into said holding tank extending longitudinally thereof, whereby said rectilinear arrangement of inletting nozzles is disposed to be marginally offset from true parallel relationship with said horizontal axis to generate a latent axial flow of fluid relative to said horizontal axis within said holding tank, directing said cross-flow spirally about the central longitudinal axis of the holding tank.
Preferably, the holding tank is provided with opposing end walls, one at each end of said tank inlet means, said walls providing a surface to reflect the latent axial flow of fluid along said holding tank, thereby generating transversely and vertically directed eddy currents at axially spaced apart locations along the surface of said holding tank to focus cross-flow of fluid carrying suspended solids to the top of said holding tank and towards said one side, between successive eddy currents.
Preferably, a plurality of holding tank modules are disposed in sequential and longitudinally contiguous relationship with each other to define a continuous passage between the holding tank modules, whereby fluid in one holding tank module can flow without restriction to an adjacent holding tank module, and vice versa, and wherein said tank inlet means within adjacent holding tank modules is alternately arranged so that said latent axial flow of fluid in one said holding tank module is opposingly directed relative to said latent axial flow of fluid in an adjacent said holding tank module, thereby generating transversely and vertically directed eddy currents at axially spaced apart locations along the surface of each said holding tank module to focus cross-flow of fluid carrying suspended solids to the top of respective said holding tanks and towards said one side thereof between successive eddy currents.
Preferably, the system includes a buffer tank communicating with the filtering means and being connected to said recirculating means separately of said filtering means to supply fluid for inletting into said holding tank separately of said filtering means, thereby providing a separate and parallel flow of fluid to the flow of fluid through said filtering means, said buffer tank having sufficient headroom to receive and accommodate a sudden oversupply of fluid from said holding tank into said filtering means whilst still maintaining a fluid level within said filtering area, said buffer tank being of a height less than the height of the filtering area to prevent a backflow of fluid beyond a prescribed threshold level.
Preferably, the tank discharge means includes a partition to maintain separation of the contents of the holding tank and the filtering means, and a primary lip at the top of the partition, whereby extraneous fluid from the holding tank is permitted to cascade over the primary lip and subsequently pass down through the filtering means.
Preferably, the filtering means includes a prefilter disposed adjacent to the primary lip for extracting solids from the fluid on it cascading over the primary lip prior to passing through to the filtering means, the prefilter including:
(i) a chamber for receiving and expelling liquid from the cascading flow of liquid having an anterior wall surmounted by said primary lip, a posterior wall spaced therefrom surmounted by a secondary lip and a bottom; and
(ii) a suction pipe disposed longitudinally within said chamber in parallel spaced relationship to said walls having a series of inlet holes to extract some of the liquid with entrained solids therein from said chamber.
Preferably, the prefilter includes a flow diverting means to divert and reverse the flow of fluid from the cascading flow over the primary lip so that a reversing and opposing fluid flow. is created adjacent the cascading flow from the primary lip so that a reversing and opposing fluid flow is created adjacent the cascading flow from said primary lip and upwardly along the posterior wall of said chamber. In this manner, the reversing liquid flow acts to retain solids in the cascading flow for subsequent extraction.
Preferably, the series of holes are disposed on the surface of said suction pipe at a position to confront the cascading flow to facilitate extracting solids retained therein.
Preferably, the the relative height of the secondary lip is less than the height of the primary lip so as to facilitate subsequent cascading of the reversing fluid flow over the secondary lip and into the one end of the filtering means.
In accordance with a second aspect of the present invention, there is provided a tank system for accommodating aquatic life comprising:
a holding tank for holding fluid to sustain aquatic life disposed therein;
a filtering means for receiving extraneous fluid from said holding tank at one end of a filtering area and allowing the fluid to pass through a filtering medium disposed within the filtering area to another end of the filtering area;
tank discharge means to provide for the discharge and passage of the extraneous fluid from said holding tank to the top of said filtering means;
recirculating means for recirculating the extraneous fluid passed through said filtering means, from proximate the bottom of said filtering means to said holding tank;
said filtering means being adjacent to said holding tank and said tank discharge means allowing for the natural flow of fluid from the top of said holding tank adjacent to said one side, to the top of said filtering area; and
a buffer tank being adapted to communicate with said filtering means to provide for a common supply of fluid therebetween;
wherein said buffer tank is connected to said recirculating means separately of said filtering means to supply fluid for inletting into said holding tank separately of said filtering means, thereby providing a separate and parallel flow of fluid to the flow of fluid through said filtering means, said buffer tank having sufficient headroom to receive and accommodate a sudden oversupply of fluid from said holding tank into said filtering means whilst still maintaining a fluid level within said filtering area, said buffer tank being of a height less than the height of the filtering area to prevent a backflow of fluid beyond a prescribed threshold level.
In accordance with a third aspect of the present invention, there is provided a method for accommodating aquatic life, comprising:
discharging fluid from the top and along the substantial longitudinal extent of one side of a holding tank filled with fluid in which aquatic life may be disposed;
filtering out impurities from the discharged fluid whilst gravitating through a filtering area;
recirculating filtered fluid to the bottom of the holding tank; and
inletting the recirculated filtered fluid into the tank under pressure at a position spaced from and generally parallel to where the fluid is discharged from the holding tank, so that a uniform, circulatory cross-flow of fluid is created along the longitudinal extent of the holding tank about a generally horizontal axis in substantially parallel relationship to said one side.
Preferably, the method includes inletting recirculated fluid into the holding tank from directly below where fluid is discharged, at an oblique angle relative to the horizontal and vertical, upwardly and transversely across said holding tank in a direction to promote said circulatory cross-flow of fluid.
Preferably, the method includes inletting recirculated fluid into the holding tank from a diagonally opposed position to where fluid is discharged, at an oblique angle relative to the horizontal and vertical, upwardly and transversely across said holding tank, in a direction to promote said circulatory cross-flow of fluid.
Preferably, the method includes directing fluid with more of a horizontal component from the position below from where fluid is discharged than in the case of directing fluid from the diagonally opposed position to where the fluid is discharged.
In accordance with a fourth aspect of the present invention, there is provided a method for accommodating aquatic life, comprising:
discharging fluid from the top of a holding tank filled with fluid in which aquatic life may be disposed;
filtering out impurities from the discharged fluid whilst gravitating through a filtering area;
recirculating filtered fluid to the bottom of the holding tank;
recirculating a separate and parallel flow of filtered fluid after filtering from the filtering area to the holding tank via a buffer tank;
automatically channelling excessive fluid out during the filtering and recirculating steps into said buffer tank when a sudden oversupply of fluid is discharged from said holding tank for filtering, thereby maintaining a fluid level within the filtering area at a prescribed threshold level; and
automatically feeding the excessive fluid back during the filtering and recirculating steps, as the excessive discharge volumes are diminished.